al_draw_pixel(3alleg5)                                  al_draw_pixel(3alleg5)

       al_draw_pixel - Allegro 5 API

              #include <allegro5/allegro.h>

              void al_draw_pixel(float x, float y, ALLEGRO_COLOR color)

       Draws a single pixel at x, y.  This function, unlike
       al_put_pixel(3alleg5), does blending and, unlike
       al_put_blended_pixel(3alleg5), respects the transformations (that is,
       the pixel's position is transformed, but its size is unaffected - it
       remains a pixel).  This function can be slow if called often; if you
       need to draw a lot of pixels consider using al_draw_prim(3alleg5) with
       ALLEGRO_PRIM_POINT_LIST from the primitives addon.

       · x - destination x

       · y - destination y

       · color - color of the pixel

         Note: This function may not draw exactly where you expect it to.  See
         the pixel-precise output section on the primitives addon
         documentation for details on how to control exactly where the pixel
         is drawn.

       ALLEGRO_COLOR(3alleg5), al_put_pixel(3alleg5)

Allegro reference manual                                al_draw_pixel(3alleg5)